Closed-Loop Dehydration for Mercury Removal Regeneration
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Solution Overview
Problem
Mercury removal units in cryogenic gas plants face significant costs and environmental impacts due to the practice of flaring spent, wet gas instead of recovering and recycling it for dehydration, leading to unnecessary nitrogen or process gas loss.
Innovation Solution
A closed-loop system is implemented for dehydrating mercury removal units, where spent, wet gas is recycled and compressed, then reused to regenerate the mercury adsorbent material, bypassing flaring by directing the regeneration gas stream to upstream units within the plant, allowing for continuous operation and minimizing gas loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If spent wet gas is sent to flare, then environmental compliance is simplified, but significant costs are incurred due to unrecovered nitrogen or process gas
Solution Approach 1:
The patent recovers spent wet gas from the mercury removal unit that would otherwise be discarded to flare. The system captures this gas, dehydrates it through molecular sieve vessels, and recompresses it for reuse as regeneration gas, thereby recovering valuable nitrogen or process gas and eliminating flaring costs.
Solution Approach 2:
The dehydration system is self-sufficient, using the spent wet gas from the mercury removal unit itself as the feedstock for its own molecular sieve dehydration vessels. This creates a closed-loop system where the unit dehydrates its own spent gas without requiring external dry gas sources.
2Quantity of substance
If spent wet gas is flared, then environmental penalties are avoided, but substantial cost savings are lost
Solution Approach 1:
The system prevents the harmful act of flaring by recovering and reusing the spent wet gas. Instead of burning it in a flare, the gas is dehydrated and recompressed for continued use as regeneration gas, eliminating environmental penalties while maintaining adequate regeneration gas quantity.
Solution Approach 2:
The system transforms the spent wet gas from an unwanted waste stream into a useful regeneration gas by changing its moisture content parameter through molecular sieve dehydration. This parameter change enables the gas to be reused without compromising the performance of the mercury removal unit.
3Reliability
If hot dry gas is used for dehydration, then mercury adsorbent material is effectively regenerated, but unrecovered gas incurs significant costs
Solution Approach 1:
The system uses its own spent wet gas as the feedstock for dehydration, making the regeneration process self-sufficient. The molecular sieve vessels dehydrate the spent gas from the mercury removal unit, and the regenerated gas is reused for continued dehydration operations, eliminating the need for external dry gas sources and preventing gas loss.
Solution Approach 2:
Instead of discarding the spent wet gas to flare, the system recovers it and processes it through molecular sieve dehydration. This recovery process maintains the reliability of mercury removal by ensuring adequate dehydration capability while preventing the loss of valuable nitrogen or process gas.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in substantial cost savings and reduced environmental impact by preventing gas flaring, enabling efficient reuse of nitrogen or process gas and ensuring effective dehydration of mercury removal beds without the need for additional gas sourcing.
Implementation Method 1
A condenser is in communication with the wet gas outlet of the mercury removal vessel in dehydration mode for condensing water to form a stream containing water and regeneration gas
Implementation Method 2
A separator is provided for separating the water and the regeneration gas from the stream containing water and gas thereby forming a water stream and a regeneration gas stream
Implementation Method 3
A compressor is provided for compressing the regeneration gas stream
Implementation Method 4
a pair of dehydration vessels containing molecular sieve material receives gas from a line downstream of the compressor
Implementation Method 5
a mercury removal vessel containing mercury adsorbing material for adsorbing mercury from a feed gas stream
Data Source
AI summary
Disclosed is a system in which saturated mercury adsorbent in a gas mercury removal unit is dehydrated in a LNG, LPG or cryogenic gas plant using a regeneration gas stream. Spent regeneration gas stream is then condensed and the water is removed therefrom to form a renewed regeneration gas stream in a closed loop. The regeneration gas stream is compressed and recycled to a location in the plant upstream of an acid gas removal unit or upstream of a regeneration gas dehydration unit such that the regeneration gas stream is not sent to a flare. A dehydration unit having a pair of dehydration vessels, arranged in parallel, alternating between absorption and regeneration modes, receives gas from the compressor. Conventional plants can be retrofitted to achieve improved process efficiencies, cost savings and environmental benefits.